better shape error message

[bendichter]

Motivation

fix https://github.com/NeurodataWithoutBorders/pynwb/issues/1419

How to test the behavior?

Show how to reproduce the new behavior (can be a bug fix or a new feature)

Checklist

• [ ] Did you update CHANGELOG.md with your changes?
• [ ] Have you checked our Contributing document?
• [ ] Have you ensured the PR clearly describes the problem and the solution?
• [ ] Is your contribution compliant with our coding style? This can be checked running flake8 from the source directory.
• [ ] Have you checked to ensure that there aren't other open Pull Requests for the same change?
• [ ] Have you included the relevant issue number using "Fix #XXX" notation where XXX is the issue number? By including "Fix #XXX" you allow GitHub to close issue #XXX when the PR is merged.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8b519aa) 88.65% compared to head (cd2c1a0) 88.65%.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev     #787   +/-   ##
=======================================
  Coverage   88.65%   88.65%           
=======================================
  Files          45       45           
  Lines        9451     9452    +1     
  Branches     2688     2688           
=======================================
+ Hits         8379     8380    +1     
  Misses        757      757           
  Partials      315      315           

Files	Coverage Δ
src/hdmf/utils.py	96.50% <100.00%> (+<0.01%)	:arrow_up:

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[rly]

I prefer "Any" instead of ":" to denote that any length is allowed.